2004 Indmar Assault 5.7L Throttle/Bog Issue

Since buying this boat a few years ago, our test ride went awesome (Pulled slalom skiers with no effort), but since then it hasn't ran the same way (spread out over 2 years time, but seems like forever since we used it every weekend for 8 months out of the year).

Our first issue was fuel filter. (Throttle would get lower and lower in RPM on takeoff. Eventually couldn't get above 3K RPM, then 2K, then could only idle).

Then it was idling high and puking black smoke out the exhaust. (Turned out to be throttle position sensor. Diagnosed by disconnecting the TPS cable and no
change in throttle reaction. Had to be steady on acceleration so you could get the right fuel to air ratio).
Took TPS off the intake and couldn't turn the innerds with my pinkie like I could with the new one. Real scientific I know. (seized)
Learning after replacing it and looking back, when I put the new one in, it had some spring tension, when I took the old one out, it wasn't under any
pressure/tension.

Then it was "electrical" by being a consistent hesitation around 2k RPM and couldn't hammer it down from idle or it would bog and die.
Steady throttle past 2K and then hammer down took off, but still a slow process pulling me out of the water more than it should have been.
If the driver was too anxious and put too much throttle in, it would start to pull and then bog and lots of time and energy wasted cause your attempt
was probably done that pull. (Me mostly driving, trying to get someone new to accomplish a watersport for the first time, I get over anxious and we
both get frustrated, me angry at the equipment and embarrassed).

Ruled out fuel flow issue by buying fuel gauge and constantly reading 32 PSI thru entire range. Still replaced fuel filter. Then in priming it, fuel pump
died (another $400), also blowing out the fuse (15 or 20 amp below the engine for anyone that has to find it).

Also, on return throttle to idle from running, would consistently idle high (1200 RPM). Pop the throttle and it would come back down 700 RPM. Cleaned
IAC thinking may be sticking, but it wasn't dirty to begin with. Kept thinking TPS because that was only thing I have changed before. Sprayed starter
fluid around gaskets thinking maybe air leak and computer was compensating. No changes.

Threw another $40 for TPS (thru autozone) and put it in on Fri night. Sat morning came, and told driver (wife) to hit me full throttle. We would either
both be extremely ecstatic or still scratching our head. For the first time in a long time, it pulled like a mule and ran for the reason we bought it.

So why this post? I am no mechanic. I try to save money by reading about issues and then following others suggestions. This site has been very helpful in direction for diagnosing, but I have seen plenty of posts with same motor, bog, hesitation, issue etc and several suggested tries, but no one ever posts what resolved it. As in my case, haven't they fixed it yet and just lived with it?

2 times it has been TPS related. Different issues both times. Keeping the hesitation one as a backup, but learned a ton thru the process.

Any additional info needed, I would be glad to elaborate more. Again, no mechanic, no scientific testing, just reasonable deduction on my part. Your experience may be different. Hoping that this post will help someone years down the road when they search for the same issue. Also hoping that others that had the issue read it and just forgot to update what their solution was... (Searched for parts for 1999 Chevy C1500 5.7 if it is a non-marine part).

Where did you find the fuel filter, I can't seem to find mine on a 04 Launch with the Indmar 5.7L

Thanks for the post on what solved your problem. Just curious -- would the engine diagnostics computer have shown that the TPS was out of range? Seems like these FI engines have some provisions to help with troubleshooting the electronics.... I know that it requires the correct computer to scan, but are those difficult/expensive to locate?

Being V-Drive, ours is on the starboard side. Silver canister about 3" long with rubber hose in and out. Was fastened with 2 screws to the side with clamps.

Wotan, possibly a computer might see it, but before resolving the last TPS (hesitation @ 2K RPM), they said they hooked to the electronics and didn't see anything out of ordinary (Indmar Mechanic). Wasn't there to see what they tested or did...

1 1/2 hr tow to get there and 2 wks before they looked at it. Why I will do more myself if possible as at least I am on the water to try things if I have the parts.

Don't forget to disconnect the negative side of the battery and allow the computer (ECU) to go to sleep. Our computers are smart and learn from what is happening when you run them. When you change out any sensor, the computer still needs time to correct itself and by allowing it to sit with no power to it (15 min max) you get it to reset. Just a thought.

@jzelt -
I'm really sorry I didn't see your post earlier. I'm going to reply on the assumption that this information might help someone else, even if it's too late to help you.

I had problems almost identical to yours. After replacing everything in the obvious chain of related parts (fuel pump, fuel/water separator, injectors which are ungodly expensive for all eight, other things I cannot remember -- over $3,000 by the time I was done). After all of this work and over a month of re-testing with full-blown "water tests", I finally learned it was a < $50 part.

As it turns out, there is a "fuel pickup tube" in the fuel tank that can come apart, or spring a *very small* leak over the years.

Here's the really interesting part: When you run the boat on land or to show your mechanic, it might run fine depending on how minor the problem. It won't be until your boat is *under load* (for example, a water test) that you'll see the issue, because it needs more gas, and a minor leak at this fuel-pickup becomes an issue.

We don't have a SkiersChoice mechanic locally here in West Palm Beach, FL. Technically we do have one (according to the part-time dealer here), but this mechanic doesn't return calls and he wants nothing to do with SkiersChoice boats as he's primarily doing much larger Ocean Yatchs now days. Therefore, I get my boat serviced by the local Mastercraft dealer, which I'm very happy with -- they really do great work. Sidenote: They've never given me the "Mastercarft is better than Supra" story or condescending attitude, not once in all of my visits.

My dealer called SC to order this part, and from what I understand SC does not stock it, but it's a standard part from the big wholesale marine supply place most of these guys use (I forget the name off the top of my head). My dealer told me that this part could theoretically be repaired, but in their experience, because it's in the tank, it just comes undone, no matter how much they do to re-affix it, and no matter what special equipment they use.

I'll send you a link to a similar part here (although I don't believe it's the same). The reason SC's part is unique on my Supra Launch 21V, is that it's larger than the conventional part on most other boats. For example, the link I'm attaching here is a photo of a tube with a 7/16" threaded fitting to attach the fuel-line. If I remember right, the line in my 21V was larger, something like 3/4". Whatever the size was, it was larger and less conventional.

Here's a link to the similar part, so that you can get an idea of the appearance:
http://greatlakesskipper.com/en_us/s...nk-pickup-tube

I hope this post can save someone else thousands of dollars, like it would have done for me, had I found it before replacing more expensive items!

Also, write back, and let me know if you ever fixed your issue without this. I'm curious, if this problem was not related, what else it could have been.

I appreciate the feedback from all of you on this issue as my 2004 5.7L Assault is doing the same thing. Idling at 1400 until I stab the throttle and "sometimes" she returns back to around 700 RPM's. I did have an Indmar Mechanic hook up the code reader and it threw a TPS failure code. Because of this thread, I will be replacing mine as soon as I can get to the parts store to pick one up. Thanks Guys, you have helped me out with troubleshooting this issue!